[ by C-I Staff] The equity markets have closed for the week, and Knight shares ended the day up 57% from Thursday's close.  On Wednesday and Thursday, those same shares lost about 75% of their value from Tuesday's closing price. Mathematics of a Plunge and Recovery. Now, before you go ahead and say something stupid like, "Hey, that's a net difference of only 18% - Knight's doing well," hold your thoughts to yourself and do some simple math.  You'll need to do 2 calculations:  (i) 75% of $10.33 (Tuesday's closing price), and (ii) 57% of $2.58 (Thursday's closing price). Here's how the numbers work out: By Thursday night, Knight shares suffered a 2-day loss of $7.75;  on Friday, the shares regained $1.47. Net-net, those shares are still under water by $6.28. Okay, class is over.